I put a 1TB SATA disk in a Dell server with PERC RAID controller and configured that disk as a single virtual disk (IE the disk gets a RAID signature the PERC likes and is passed through to the OS). The disk when viewed on a regular SATA controller has 1953525168 sectors, when it goes through the PERC it has 1952448512 sectors, that is 525MB less space when going through the PERC! That's 1% of a 500G SSD. Is there any way to configure PERC to reduce it? Is using "HBA" mode worthwhile? -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
On 10/9/20 10:02 pm, Russell Coker via luv-main wrote:
I put a 1TB SATA disk in a Dell server with PERC RAID controller and configured that disk as a single virtual disk (IE the disk gets a RAID signature the PERC likes and is passed through to the OS). The disk when viewed on a regular SATA controller has 1953525168 sectors, when it goes through the PERC it has 1952448512 sectors, that is 525MB less space when going through the PERC! That's 1% of a 500G SSD.
0.1%
Is there any way to configure PERC to reduce it? Is using "HBA" mode worthwhile?
If you won't be using the hardware RAID anyway, go for it. It might even alleviate the need for the RAID controller cache battery. Cheers, Andrew -- mailto:andrew@sericyb.com.au Andrew Pam https://sericyb.com.au/ Manager, Serious Cybernetics https://glasswings.com.au/ Partner, Glass Wings
On Thursday, 10 September 2020 11:40:52 PM AEST Andrew Pam wrote:
On 10/9/20 10:02 pm, Russell Coker via luv-main wrote:
I put a 1TB SATA disk in a Dell server with PERC RAID controller and configured that disk as a single virtual disk (IE the disk gets a RAID signature the PERC likes and is passed through to the OS). The disk when viewed on a regular SATA controller has 1953525168 sectors, when it goes through the PERC it has 1952448512 sectors, that is 525MB less space when going through the PERC! That's 1% of a 500G SSD.
0.1%
OK, when having the correct order of magnitude it isn't so bad.
Is there any way to configure PERC to reduce it? Is using "HBA" mode worthwhile?
If you won't be using the hardware RAID anyway, go for it. It might even alleviate the need for the RAID controller cache battery.
The cache battery shouldn't be "needed" in any case, without the battery the RAID controller for RAID 0 and 1 works just like regular hard drive controllers, writes stuff to disk and tells the OS when it's done. With the battery it can write to cache and tell the OS that a synchronous write is already committed and then use the elevator search algorithm to write them efficiently later on. Another benefit of the battery is that for RAID 5 and 6 a partial stripe write can be done synchronously and rapidly. Without the battery it is difficult to impossible to write part of the RAID 5/6 stripe without the risk of corrupting unrelated data in the event of power failure. Anyway the reason I asked on the list is that I did a quick Google of the issue and saw some results indicating problems with Linux. What I might do from now on is partition SSDs with swap space at the end of the disk. Then if I move it from a regular controller to something like a PERC the swap partition gets truncated and can be fixed with fdisk afterwards. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/
On 11/9/20 12:29 am, Russell Coker wrote:
What I might do from now on is partition SSDs with swap space at the end of the disk. Then if I move it from a regular controller to something like a PERC the swap partition gets truncated and can be fixed with fdisk afterwards.
That's a good idea! On systems with substantial amounts of RAM I've moved to putting swap on zram instead of on disk. Even faster than SSD! Cheers, Andrew -- mailto:andrew@sericyb.com.au Andrew Pam https://sericyb.com.au/ Manager, Serious Cybernetics https://glasswings.com.au/ Partner, Glass Wings
participants (2)
-
Andrew Pam -
Russell Coker